Study of ferrofluids by Mössbauer spectroscopy

The parameters of the log-normal size distribution of a MnFe₂O₄ ferrofluid powder sample have been determined by X-ray diffraction. The mean blocking temperature was determined from the maximum of _Xi. Mössbauer spectra at 4.2–300 K are interpreted by a new simple theory of superparamagnetism and taking a reduction of the internal magnetic field for small particles, a size dependence of the anisotropy constant, the size distribution and collective excitations into account.